To make a long story short, it was the DDE causing the SES light for "Zero Volume Adaptation".
What caused the DDE to fail? According to BMW Engineering, faulty Engine Harness was to blame for the DDE electronic failure.
If you see the pattern of the visits, DDE was replaced once before the Engine Harness replacement, however, that new DDE was also damaged by a short circuit due to the engine harness after 1000 miles or so, causing it to fail.

Now that everything is in place, lets see how it goes. 300+ miles and no issues. The car is driving like it should.

So if it is the ENGINE HARNESS causing the DDE failures, shouldn't there be a Technical Service Bulletin from BMW? Is the harness also causing other part(s) to fail?

As you can see, the dealer had to keep throwing parts at the car as per BMW Engineering to finally get to the bottom of this.

Regarding the build up in the intake, intake valves, and cylinder head: This is a result of the electronic EGR functionality. Is there a way around it? Only way would be to "tune it out". The stock setting for the AIR to EGR ratio needs to be modified. BMW did redesign and reprogram the EGR operation, however there isn't any data yet available if this solved the excessive soot/tar build up.

It's been a long journey for me (5 months) to get this 335D back in my hands fixed. Hopefully this never happens again to me, and if it is happening to you, hopefully I have shed some light on this issue.